In recent years pipes and conduits have been largely constructed of synthetic plastics, especially fiber-reinforced composites, or fiber-reinforced piping. These materials are far less susceptible to corrosion than metal pipe, and a pipe constructed of fiberglass reinforced plastic generally weighs only about one-fifth as much as its steel equivalent. Fiberglass piping, and piping systems made of corrosion resistant resins are extensively used in the transport of corrosive chemicals.
In the construction of a fiberglass piping system it is not only necessary to form straight tubes, but also connectors and fittings. These components are of laminar construction and constituted of an inner layer which interfaces with the transported flowing fluid. The inner layer is formed by placing a layer relatively rich in resin, with relatively low fiberglass content, directly upon a mold, or mandrel, since the inner surface of the composite is that which will come into intimate contact with the transported chemical fluid. The next, and subsequent layers of the composite are less rich in resin, and have higher concentrations of fiberglass to provide strength to the composite. Thus, the inner layer has a low fiberglass:resin ratio, and the outer layer, or layers, a high fiberglass:resin ratio. In forming composites, the layers are often applied as strips and mats, or both, wrapped about a mold, or mandrel, and impregnated with resin to form the fiber-resin layers. The fibers of adjacent layers are generally laid in different directions, or orientations, and then set, or cured and hardened to attain a mechanically strong finished composite. The finished composite is then separated from the mold.
Whereas straight fiberglass reinforced resin composite tubes have been readily fabricated in this manner, and are easily separated from the mandrel, the formation and separation of elbow-shaped connections, and fittings, have not. Whereas laminar, fiberglass reinforced resin composite tubes have been formed, e.g. on an elbow-shaped steel pipe rotated via an end affixed to a motor shaft, which provided the annular molding surface, and the tubular structure thereafter separated therefrom - this is done only with much difficulty; and with many disadvantages. Albeit the motor rotates the elbow-shaped mold, or mandrel, and thus provides a machine having the needed winding motion, the fiberglass, as a matting, must be applied by hand. This results in increased manual labor, and cost. The matting itself is expensive; more expensive e.g. than a roving, and of lower mechanical strength. There is thus an acute need to the industry for better means for forming fiber-reinforced resin composite tubes of elbow shape, and for the separation of completed elbow-shaped fiber-reinforced resin composite tubes from an annular molding surface.